Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2002-12-24
2004-09-14
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S175000, C333S167000
Reexamination Certificate
active
06791436
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrical signal filter with an improved isolation shield for magnetically isolating electrically interconnected filter sections from one another. The present invention also relates to a modular electrical signal filter and filter assembly whose component parts can be assembled without the use of solder.
BACKGROUND OF THE INVENTION
Various types of electrical signal filters are used in the CATV industry for controlling, on a frequency basis, the propagation of signals through a cable line. One example of such a filter is disclosed in U.S. Pat. No. 4,451,803, the entirety of which is incorporated herein by reference. The '803 patent discloses a split tuning filter of the type that is commonly referred to as a notch filter, for removing a selected frequency or band of frequencies from a CATV signal. With reference to
FIG. 7
, the split tuning filter includes a common circuit board
100
having first
102
and second
103
filter sections formed thereon by discrete electronic components such as inductors, capacitors and the like (not shown). Isolation shields
104
,
105
are arranged at a midpoint along circuit board
100
to provide magnetic isolation between first filter section
102
and second filter section
103
. Each shield includes a radially extending disc section
106
and a longitudinally extending flange section
107
. A slot
108
is formed in each shield, to allow the remaining, unslotted portion of disc
106
to slide into a corresponding slot
101
formed in circuit board
100
. One of the shields is pressed into a slot formed on one side of the circuit board, and the other shield is pressed into a slot formed on an opposed side of the circuit board, as shown in FIG.
7
. As explained in the '803 patent, this arrangement prevents any “line of sight” communication between components in the first and second filter sections.
Once the shields
104
,
105
are positioned on opposite sides of circuit board
100
, the circuit board is inserted into housing
109
, the open end of which is closed by filter cap
110
. This subassembly is then inserted into a tube sleeve housing (not shown) to form the final sealed filter structure.
While the filter disclosed in the '803 patent is highly successful in providing magnetic isolation between the first
102
and second
103
filter sections, there are several drawbacks associated with the use of shields
104
and
105
. First, the shields must be soldered not only to circuit board
100
, but also to filter housing
109
, in order to ground the circuit board. While the shields can be soldered to circuit board
100
with relative ease, it is relatively difficult to solder the shields to filter housing
109
once the shields are positioned within the confines of the housing. In order to achieve this type of soldering operation, it is necessary to apply a high heat source to the exterior of filter housing
109
, which can adversely effect the characteristics of the electrical components already positioned on circuit board
100
. It is also difficult to control the flow of solder within the confines of filter housing
109
, and thus it is not uncommon for one or both sides of the filter to become shorted. Such shorted filters must, of course, be discarded.
Another problem relates to flange
107
. The flange is present on each shield in order to guide circuit board
100
into filter housing
109
and to provide a soldering surface parallel to the wall of filter housing
109
. The electronic components on the circuit board, however, must be spaced away from the shields by a distance greater than the longitudinal length of flange
107
to allow the shields to be inserted into slots
101
on opposite sides of circuit board
100
. The longitudinal length of flange
107
, therefore, unnecessarily increases the overall length of the filter. This problem is even more noticeable in six-pole and eight-pole filters, which use multiple shields.
Yet another problem is that the shields, being separate components, increase the total number of components that must be handled during assembly of the overall filter device. This in turn increases manufacturing time and expense.
Yet another problem with the prior art filter shown in
FIG. 7
is that the end cap
110
must be soldered to the filter housing
109
in order to prevent rotation of the end cap
110
independent of the filter housing
109
. Since the filter is rotatably installed as a unit, it is unacceptable if one part of the filter is able to rotate independent of other parts of the filter. This necessary soldering step adds expense to the overall filter assembly. Although electronic components of the circuit board
100
are soldered in place, that soldering step can be performed in a very efficient, mass-production scale prior to assembly of the filter components into the final filter product.
In order to ensure a good ground contact between the circuit board
100
, the shields
104
and
105
, and the housing
109
, it is also necessary to solder the shields to the board to the housing during assembly of the filter. This soldering step also adds expense to filter assembly, and can be quite difficult, since the shields are positioned inside the filter housing
109
during the soldering operation.
Another problem prevalent in the CATV filter industry is that each distinct filter application currently requires a distinctly accommodating filter housing. Given the vast number of different types of filter applications, it has become necessary to design, manufacture, and maintain sufficient inventories of each individual type of filter housing for each of the different filter application products offered. This can be particularly inconvenient and expensive for electronic signal filter providers that offer a wide variety of products for a wide variety of applications.
For example, providing the machinery and manpower required to machine a large number of different filter housings having different design specifications and considerations can be an expensive undertaking. Even when the filter housing is designed to be formed by casting rater than being produced using machining techniques, producing a large number of different filter housings nonetheless mandates the use of many different manufacturing molds.
Moreover, different filter housing configurations may require different manufacturing steps to complete the assembly of the final electronic signal product, depending on the structural design. As mentioned above, additional manufacturing processes, such as manual assembly or soldering steps, drive up the cost of the final products, introduce additional opportunities for quality control issues to arise, and further complicate the manufacturing process. Accordingly, the need to manage and control the varying specifications and requirements for production of varying design applications involves increased manpower and equipment required to monitor and ensure quality, which ultimately increases production costs. Additionally, the expenses associated with providing storage facilities and logistics support in the form of personnel, equipment and for complex inventory management are another cost aspect that increases the costs of the final filter products.
It would be desirable to provide an electrical signal filter having isolation shields that are easy to handle and solder within the filter housing. It would be more desirable to provide an electrical signal filter whose component parts can be assembled into the final filter product without any soldering steps. It would also be desirable to provide a “universal” modular filter housing that can be used for any filter application, either alone as a single modular unit or in combination with a plurality of other modular units. It would also be desirable to provide modular filter components that can be assembled into the desired filter assembly configurations without any soldering steps.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an electrical sign
Maguire Joseph N.
Zennamo, Jr. Joseph A.
Burr & Brown
Eagle Comtronics, Inc.
Pascal Robert
Takaoka Dean
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